[crypto] Allow signed timestamp error margin to be configured at build time

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/crypto.h

+#ifndef CONFIG_CRYPTO_H
+#define CONFIG_CRYPTO_H
+
+/** @file
+ *
+ * Cryptographic configuration
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/** Margin of error (in seconds) allowed in signed timestamps
+ *
+ * We default to allowing a reasonable margin of error: 12 hours to
+ * allow for the local time zone being non-GMT, plus 30 minutes to
+ * allow for general clock drift.
+ */
+#define TIMESTAMP_ERROR_MARGIN ( ( 12 * 60 + 30 ) * 60 )
+
+#include <config/local/crypto.h>
+
+#endif /* CONFIG_CRYPTO_H */

src/crypto/ocsp.c

 #include <ipxe/base64.h>
 #include <ipxe/uri.h>
 #include <ipxe/ocsp.h>
+#include <config/crypto.h>
 
 /** @file
  *
 	/* Check OCSP response is valid at the specified time
 	 * (allowing for some margin of error).
 	 */
-	if ( response->this_update > ( time + X509_ERROR_MARGIN_TIME ) ) {
+	if ( response->this_update > ( time + TIMESTAMP_ERROR_MARGIN ) ) {
 		DBGC ( ocsp, "OCSP %p \"%s\" response is not yet valid (at "
 		       "time %lld)\n", ocsp, x509_name ( ocsp->cert ), time );
 		return -EACCES_STALE;
 	}
-	if ( response->next_update < ( time - X509_ERROR_MARGIN_TIME ) ) {
+	if ( response->next_update < ( time - TIMESTAMP_ERROR_MARGIN ) ) {
 		DBGC ( ocsp, "OCSP %p \"%s\" response is stale (at time "
 		       "%lld)\n", ocsp, x509_name ( ocsp->cert ), time );
 		return -EACCES_STALE;

src/crypto/x509.c

 #include <ipxe/rootcert.h>
 #include <ipxe/certstore.h>
 #include <ipxe/x509.h>
+#include <config/crypto.h>
 
 /** @file
  *
 	struct x509_validity *validity = &cert->validity;
 
 	/* Check validity period */
-	if ( validity->not_before.time > ( time + X509_ERROR_MARGIN_TIME ) ) {
+	if ( validity->not_before.time > ( time + TIMESTAMP_ERROR_MARGIN ) ) {
 		DBGC ( cert, "X509 %p \"%s\" is not yet valid (at time %lld)\n",
 		       cert, x509_name ( cert ), time );
 		return -EACCES_EXPIRED;
 	}
-	if ( validity->not_after.time < ( time - X509_ERROR_MARGIN_TIME ) ) {
+	if ( validity->not_after.time < ( time - TIMESTAMP_ERROR_MARGIN ) ) {
 		DBGC ( cert, "X509 %p \"%s\" has expired (at time %lld)\n",
 		       cert, x509_name ( cert ), time );
 		return -EACCES_EXPIRED;

src/include/ipxe/x509.h

 	struct x509_time not_after;
 };
 
-/** Margin of error allowed in X.509 response times
- *
- * We allow a generous margin of error: 12 hours to allow for the
- * local time zone being non-GMT, plus 30 minutes to allow for general
- * clock drift.
- */
-#define X509_ERROR_MARGIN_TIME ( ( 12 * 60 + 30 ) * 60 )
-
 /** An X.509 certificate public key */
 struct x509_public_key {
 	/** Raw public key information */